1. Field of the Invention
The present invention relates to an entrance/exit piping structure for an intercooler, in an intake system of an internal combustion engine, for cooling pressurized air fed from a supercharger to the intercooler and then to an engine body.
2. Description of the Related Art
Generally, to increase an engine output, a large amount of air is fed to the engine through a supercharger. However, as air is compressed in the supercharger, the temperature of the air rises to, for example, approximately 180° C. To supply the pressurized air to the engine body after cooling the air to increase the density thereof, an intercooler is used.
In such a case, the intercooler is disposed on the front of a radiator. That is, there are arranged the intercooler, the radiator, a cooling fan and the engine body in this order from a front side of a vehicle. On the other hand, as the supercharger is driven by the engine or by exhaust gas from the engine, it is disposed in the vicinity of the engine body. Accordingly, a piping structure for connecting the intercooler with the supercharger and with the engine body is shaped to cross the radiator.
Also, the radiator is generally mounted on the vehicle so that upper and lower tanks (header tanks) are disposed in the upward/downward direction, while the intercooler is selected to be either a vertical type wherein a pipe section is disposed in the upward/downward direction or a horizontal type wherein a pipe section is disposed in the leftward/rightward direction in accordance with the space in the engine compartment. The present invention relates to an improvement in the entrance/exit piping structure of the intercooler when the horizontal type intercooler is adopted. There is usually little room in the engine compartment in the horizontal direction.
In the prior art, an entrance/exit pipe 2 of an intercooler 1 is formed to have a portion bending approximately 90° as shown in FIG. 8 to allow it to pass through a slight gap between the upper part of the radiator 3 and the body frame or a bonnet. In this case, as it is difficult to bend a thick and round pipe to have such a severe curvature as well as to pass the same through the small gap, the bending portion 2a of the entrance/exit pipe 2 is formed to be of a flat shape as shown in FIG. 9 in an enlarged manner. Thereby, the entrance/exit pipe 2 is easily bendable and is capable of avoiding interference with the radiator 1, or other parts, when the intercooler 1 is mounted on the vehicle.
However, in view of environmental problems, the emission regulation of emission gas from diesel engine has recently been strict more and more. For instance, as shown in FIG. 10, in Europe, the limit on NOx in the exhaust gas from a large-sized truck, which was 5 (g/kwh) in EURO 3, is now 3.5 (g/kwh) in EURO 4 and will be 2 (g/kwh) in EURO 5 which is expected to start from 2008. Also, a PM (particulate matter) value which was 0.1 (g/kwh) in EURO 3 will be 0.02 (g/kwh) in EURO 5.
To satisfy these limits, it will be necessary to increase the pressure of pressurized air output from the supercharger, which is 1.8 (kgf/cm2) at present, to 2.7 (kgf/cm2) and finally to 3.6 (kgf/cm2) and also to increase the temperature of the pressurized air, which is 180 (° C.) at present, to 204 (° C.) and finally to 239 (° C.).
Accompanied with such increase in supercharged air pressure and temperature, a problem will occur in the conventional entrance/exit piping structure wherein the bending portion of the intercooler is flattened (particularly, in the entrance piping structure); that is, the strength becomes insufficient and this portion is liable to deform or broken. To increase the strength, it will be necessary to provide ribs in a pipe wall or pillars in the interior of the pipe, which would result in an increase in cost or in difficulty in the molding process.